Controlled Growth of the Inorganic Backbone in Low-Dimensional Perovskites for Efficient, Stable, Semi-Transparent Wide Bandgap Perovskite Solar Cells

Abstract Wide bandgap (WB) perovskites are of interest for envisioned applications in coloured and semi-transparent solar cells. For this, phase pure low dimensional perovskites (LDP) are of promise as they pair a tuneable wide bandgap with stability. However, so far, the power conversion efficiency (PCE) of LDP solar cells barely touched a few percentages, mainly due to inefficient charge transport being the inorganic layer spaced by organic sheets. To overcome such limit is essential to control the growth of the crystalline backbone, which is dictated by the alignment of the inorganic planes. Here, we demonstrate an effective strategy, based on the judicious choice of additives and controlled seed growth in the perovskite solution, to guide the crystallization of phase pure LDPs inorganic layers perpendicularly to the substrate. The vertically aligned LDP solar cells with only two inorganic layers held together (refereed to n = 2) and a bandgap of 2.0 eV, outperformed their non-oriented 2D counterpart, boosting the PCE to a record value of 9.4%. Furthermore, this sets a benchmark for the stability of WB PSCs, where 80% of the initial performance was retained after ~ 100 h illumination. To broaden the scope of our method, we fabricated semi-transparent LDP devices (transmittance > 30%) with a PCE of 6% paving the way for the development of tuneable smart solar devices.